In the discussion of the background that follows, reference is made to certain structures and/or methods. However, the following references should not be construed as an admission that these structures and/or methods constitute prior art. Applicants expressly reserve the right to demonstrate that such structures and/or methods do not qualify as prior art.
Cutting tools for the chipforming machining of metallic workpieces typically employ a cutter body on which are mounted cutting inserts of thin, polygonal shape, such as rectangular (square or non-square) and triangular. Such inserts have top and bottom surfaces interconnected by a side surface that intersects the top surface to form cutting edges therewith.
For example, in a long edge milling cutter, the cutting inserts are arranged in respective insert seats on a cutter body such that one of the cutting edges of each insert is positioned to constitute an active cutting edge and is oriented generally in the fore-aft direction, i.e., generally radially relative to the longitudinal axis of the cutter body. Those cutting edges are generally aligned to form helical cutting flutes which cut a workpiece when relative rotation between the cutter body and the workpiece occurs about the longitudinal axis of the cutter body. In addition, each of the frontmost, or end, inserts on the cutter body has an active front cutting edge oriented transversely relative to the longitudinal axis. During a cutting operation, all of the cutting inserts are subjected to forces in the radial inward direction of the cutter body which can be resisted by mounting inserts such that they bear against a radially outwardly facing surface of the cutter body. In addition, the end inserts are further subjected to substantial forces in the axially rearward direction of the cutter body, due to the presence of their active transverse cutting edges.
The axially rearward forces applied to the end inserts may not be completely resisted by the mounting screw, but can be further resisted by abutting the inserts against axially forwardly facing support walls of the cutter body. However, that increases the amount of material for fabricating the cutter body, and may interfere with chip formation on adjacently located inserts. Also, by configuring such support walls to conform to the shape of the abutting face of the abutting insert, it may occur that the cutter body is prevented from accommodating a wide variety of shapes.
It has also been proposed to resist the axial force acting on an end insert by providing the bottom surface of the insert with a recess, e.g., of generally pyramidal shape, which seats on a correspondingly shaped upward protrusion of the insert seat (e.g., see U.S. Pat. No. 7,819,610). However, such an arrangement has met with only limited success.
In the case of high-speed cutters which cut relatively light-weight materials such as aluminum, the inserts are subjected to high centrifugal forces. It has been proposed to resist such centrifugal forces by providing the bottom surface of the cutting insert with serrations oriented parallel to the longitudinal axis of the cutter body, which serrations mesh with corresponding serrations formed in the insert seat (e.g., see U.S. Pat. No. 6,921,234). However, such serrations would not effectively resist the axial forces applied to the end inserts of a lower-speed cutter which cuts heavier-weight materials.
In U.S. Pat. Nos. 6,146,060 and 7,585,137, it has been proposed to provide the bottom surface of a cutting insert with two sets of serrations, with the serrations of each set oriented parallel to one another and perpendicular to the serrations of the other set. Those opposing sets of serrations mesh with corresponding serrations formed in the seat and thus offer resistance to cutting forces applied in different directions, e.g., axial and radial directions. Although being effective, inserts of that type are relatively difficult and expensive to manufacture. Also the total force-resisting surface area defined by each set of serrations is reduced, due to the presence of the other set of serrations. In addition, it will be appreciated that once the insert is mounted, it is locked against movement in any direction, eliminating the ability of pressing the insert against a surface of the cutter body, e.g., by a mounting screw, for maximizing the insert's stability.
The insert seats can be formed directly on the cutter body, or by means of a separate shim interposed between the insert and the cutter body. Such a shim offers a certain degree of protection for the cutter body in the event of a catastrophic failure of the cutting insert during a cutting operation.
It is apparent from the foregoing discussion that it would be desirable to provide cutting inserts with better support against axially rearwardly directed forces.